1. Field of the Invention
The present invention relates to a visual navigation system and a method thereof. More particularly, the present invention relates to a visual navigation system and method capable of guiding robots by use of structured light.
2. Description of Related Art
Recently, with the rapid progress of sensors and control theories, an intelligent robot system originally employed in an automatic factory field has been gradually applied to various service applications, which opens up a new field of robot autonomous services. The research and development of service robots are mainly carried out by academic institutions in the past, but now they are paid more and more attention by the industry. The main reasons for the creation of in-door service robots include: 1. people want to get rid of some annoyed and boring repetitive work, such as housework and cares for the sick; 2. the cost of various electro-mechanical apparatus drops. Currently, many industrial analyses point out that, it is a prosperous technical field to utilize robots to release people from housework, which will bring great business opportunities.
In the robot system, autonomous navigation is a core technique, including wide-area positioning, obstacle detection, and path routing and tracking. At present, the biggest bottleneck for the navigation technique is that, during the navigation, the robots usually cannot anticipate or identify a dynamically changing environment. Furthermore, since the data obtained by sensors is usually incomplete, discontinuous, and unreliable, the environment-sensing capability of the robots is diversified but not robust. The robot's autonomous navigation is mainly divided into two categories; one is a visual navigation system and the other is a non-visual navigation system. The former employs a visual sensor to capture data in a unit of “surface”, which has a wide sensing range and can obtain most of the environment information. Whereas, the latter obtains sensing signals in a unit of “point” or “line”, in which the characteristics of different sensors may influence the navigation effect. For example, an ultrasonic sensor has a large sensing angle, a low resolution, but cannot obtain the specific shape of an obstacle; and, an infrared sensor is easily interfered by the surface characteristics of the obstacle. Currently, multi-sensing modes are combined to eliminate disadvantages of a single sensor, but the complexity of the system is accordingly increased and the power consumption is increased as well.
As for the current visual navigation methods, for example, PRC Patent No. CN1569558A discloses a robot visual navigation method using picture characteristics, which makes a full play of the advantages of image sensing, and obtains most of the environment information. In terms of the navigation function, the above method is capable of achieving a more desirable navigation effect in a non-structural space, compared with other sensors such as laser, infrared, or ultrasonic sensors. However, the aforementioned patent employs plenty of operation resources to capture feature objects in the environment such as doors, pillars, corners, or other man-made signs, then compares the identified scene image neighbouring the signs with an original map image to identify the position of the robot, and finally determines a moving direction and speed of the robot. In the applications of in-door robots, for example, clean-service robots, the aforementioned navigation method may reduce the overall navigation efficiency due to the image processing, which is also unsatisfied in evading obstacles.
As for the current non-visual navigation methods, for example, PRC Patent No. 1925988 discloses a robot navigation system and a floor material for providing absolute coordinates used by the robot navigation system. The navigation system has two-dimensional (2D) barcodes, a barcode reader, and a control unit. The 2D barcodes are formed at predetermined intervals on a floor with a predetermined size, and have different unique coordinates, respectively. The barcode reader is installed in a robot for reading the coordinates represented by the 2D barcodes on the floor, and then, the control unit performs subsequent a movement control according to the coordinates. However, the floor material adopted by the patent should be particularly manufactured, which has a high cost and easily damaged to cause the failure of the navigation. Moreover, the floor material may even be seriously damaged to cause the robot to sink therein and result in malfunctions.
Although the robot navigation methods provided by the above two patents can solve a part of the navigation problems, as for in-door service robots, the following problems still exist.
1. The robot cannot work in darkness, so the problem that an ordinary visual servo easily fails in an environment of low illumination should be overcome.
2. The operations for determining the position of an obstacle and routing a path are rather time-consuming, and an over-high operation ratio of the visual servo may seriously influence the instantaneity of the servo control.
3. All the paths are formed through using a visual servo, and the tracking of the robots is of an excessively low precision at far away positions in the image.
4. The wandering paths for autonomously moving robots are repeated, which wastes time and power.
5. An additional visual servo system usually needs to be constructed in the environment, which may affect the original layout and raise the cost of the system.
Therefore, a visual navigation system and method capable of solving the above five problems in visual navigation are needed to achieve rapid progress in the development of in-door service robots, so as to provide more reliable services for the people.